由于点位变动、破坏等原因，会遇到已测设的定向附合边精度不再满足规范规定或附合边不再存在的问题。在无法或无需重新测设附合边的情况下，就只能采用无定向导线测量形式。结合广州地铁测量案例，介绍了无定向导线的计算方法和精度特点，对无定向导线在地铁的应用进行探讨。得出以下结论： 1）用无定向导线复测精密导线网，可减少因定向附合边方位变动所引起的误差； 2）用无定向导线确定盾构定向是一种有效且精度较高的方法，是地下定向测量的有效补充； 3）用无定向导线进行区间贯通联测可提高控制点相对精度，有利于控制基标的测设和检测。

Due to the change or damage of the survey points, the precision of the oriented boundary surveyed can not meet the requirements of relevant standards, or the oriented boundary disappear. Under such circumstance, nonoriented traverse surveying technology may be used. The calculation methods and precision of nonoriented traverse are presented, and the application of nonoriented traverse in the survey of Guangzhou Metro is discussed. Conclusions drawn are as follows: 1) The error induced by direction changing of oriented boundary can be reduced by using nonoriented traverse. 2) The nonoriented traverse surveying method is an effective method, which has high precision in shield orienting. 3) The nonoriented traverse surveying method can improve the relative precision of control points in the breakthrough survey of running tunnel.